1. Field of the Invention
The present invention relates to a method of determining whether a MEMS device is hermetic, and more particularly, to a method of determining whether a MEMS device is hermetic by applying multiple voltage differences between a movable part and a sensor electrode to measure multiple effective capacitances of the MEMS device, so as to evaluate a symmetry of a capacitance-to-voltage curve of the MEMS device.
2. Description of the Prior Art
MicroElectroMechanical System (MEMS) device is a special type of integrated-circuit (IC), which detects displacement behaviors of a movable part to derive acceleration or angular speed of an electronic device, thereby operates as an accelerometer or a gyroscope.
To improve sensitivity and accuracy of the MEMS device, the movable part is hermetically encapsulated in a package to ensure the displacement behaviors of the movable part is free from contaminants such as dust and water vapors. Based on different designs and application requirements, the package can be filled with inert gas or evacuated to vacuum to build the hermetic system with different pressures and desired operational characteristics. Meanwhile, the hermetic system further ensures the reliability and endurance of the MEMS device since it is waterproof and/or anti-oxidation to protect the MEMS device from damage. Therefore, once the hermeticity of the MEMS device is broken, a proper and sensitive waning indication is required.
Currently, the hermeticity of the MEMS device is mostly detected by measuring electronic characteristics, such as a leakage current, of the MEMS device. Also, the hermeticity influences a frequency response associated with Q-factor of the MEMS device, so the hermeticity of the MEMS device can be detected by measuring the frequency response associated with Q-factor.
However, the two measurements above mentioned are difficult to perform and with low sensitivity. Consequently, there is a need to improve the prior art.